Method of making a creep resistant lead alloy

ABSTRACT

The present invention comprises a creep resistant lead base alloy characterized by finely dispersed intermetallic compound and containing, by addition, at least one solid soluble alkali or alkaline earth metal component prealloyed with lead which is selected from Groups IA and IIA of the Mendeleeff Periodic Chart of the atoms, and at least one metalloid component selected from Group VB of said atomic chart, the balance being essentially lead, and a method of preparing said alloy. The method of making said creep resistant lead base alloy comprises: (a) dissolving the selected alkali or alkaline earth metal in molten lead, (b) particulating the mass from the molten form to provide a prealloy, (c) intimately and homogenously contacting said solid, particulate prealloy with the metalloid component, and (d) diffusing said metalloid component into the prealloy at an elevated temperature to form an essentially insoluble intermetallic compound finely dispersed throughout a final creep resistant lead base alloy.

Unite States Patent Foerster et a1.

METHOD OF MAKING A CREEP RESISTANT LEAD ALLOY Inventors: George S. Foerster; Garth D. Lawrence,

both of Midland, Mich.

The Dow Chemical Company, Midland, Mich.

Filed: Apr. 24, 1970 Appl. No.: 31,801

Assignee:

Related U.S. Application Data Division of Ser. No. 679,621, Nov. 1, 1967, abandoned.

References Cited UNlTED STATES PATENTS [451 Jan. 25, 1972 Att0rneyGrisw0ld and Burdick and John M. DeMeester [5 7] ABSTRACT The present invention comprises a creep resistant lead base alloy characterized by finely dispersed intermetallic compound and containing, by addition, at least one solid soluble alkali or alkaline earth metal component prealloyed with lead which is selected from Groups 1A and 11A of the Mendeleefr" Periodic Chart of the atoms, and at least one metalloid component selected from Group VB of said atomic chart, the balance being essentially lead, and a method of preparing said alloy. The method of making said creep resistant lead base alloy comprises: (a) dissolving the selected alkali or alkaline earth metal in molten lead, (b) particulating the mass from the molten form to provide a prealloy, (c) intimately and homogenously contacting said solid, particulate prealloy with the metalloid component, and (d) diffusing said metalloid component into the prealloy at an elevated temperature to form an essentially insoluble intermetallic compound finely dispersed throughout a final creep resistant lead base alloy.

13 Claims, No Drawings METHOD OF MAKING A CREEP RESISTANT LEAD ALLOY This application is a division of Ser. No. 679,621, filed Nov. l, 1967 and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to creep resistant lead alloys and a method of preparing said lead base alloys.

2. Prior Art Heretofore the design utility of lead in many applications has been limited by its high creep rate at room temperature. While the creep resistance of lead may be increases somewhat by alloying certain elements therewith which cause precipitation hardening, e.g., calcium and antimony, in many cases the creep resistance is still insufficient. More recently the creepresistance of lead had been improved by fabricating lead from a very fine powder, but such powder is expensive and hazardous because of its toxicity.

A primary object of the present invention, therefore, is to provide a novel creep resistant lead base alloy.

Another primary object of the present invention is to provide a novel method of preparing a creep resistant lead base alloy.

A further object of the present invention is to provide a novel method of preparing a creep resistant lead base alloy which avoids the need to use extremely fine lead powder.

THE INVENTION In accordance with the present invention the above and other objects and advantages are obtained in method of preparing a creep resistant lead base alloy which comprises: dissolving particular solid soluble alkali or alkaline earth metals selected from Groups IA and IIA of the Mendeleeff Periodic Chart of the atoms in molten lead, particulating the resultant alloy from the molten form to provide a prealloy, intimately and homogeneously contacting said particulate prealloy with particular metalloid elements selected from Group VB of said atomic chart, and diffusing said element into the prealloy at an elevated temperature to form an essentially insoluble intennetallic alloy phase finely dispersed throughout the resulting final creep resistant lead base alloy.

Among the advantages of the method of the present invention is that it produces a very fine dispersion of the intermetallic compound in the lead matrix, the interparticle spacing being less than about 5 microns and preferably less than 0.5 microns. If, on the other hand, the solid soluble alkali or alkaline earth metal selected from Groups IA and IIA and the element selected from Group VB were conventionally added to a single lead melt, the final alloy on solidification would not contain the fine dispersion of intermetallic particles due to precipitation of the insoluble intermetallic in the melt and segregation at its surface before solidification. Another advantage of the method of the present invention is that it does not require the use of the ultra fine lead powder which is expensive and somewhat hazardous.

In practicing the method of the present invention a lead base prealloy is first prepared by dissolving in either pure or commercial grade molten lead, containing the normal amounts and types of impurities, at least one alkali or alkaline earth metal selected from the aforesaid Group IA and IIA elements in an amount of from about 0.01 to about 5.0 weight percent. Preferably, the Group IA and IIA additive metal will be selected from the following elements, in a percentage amount by weight (based on the total weight of the final alloy) within the broad and preferred ranges indicated below.

Alkali or Alkaline Earth Element Broad range Preferred Range Calcium 0.0 |-O.7 0.05-0.5 Lithium 0.0 l0.7 0.05-0.5 Magnesium 0.01-1.5 0.54.0 Sodium 0.0 l2.0 0.5-1.5

In preparing the aforesaid lead base prealloy (using techniques and equipment commonly employed in the lead art) commercially pure lead is heated and liquified at a temperature, e.g., from about 650 F. to about l,000 F., sufficient to dissolve essentially all the selected alkali or alkaline earth element. Said element may be admixed therewith either in particulate form or by introducing small ingots or chunks thereof into the molten lead while the molten mass is continually stirred to facilitate dissolution. It may also be desirable to hold the additive metal below the melt surface until solution occurs to avoid excessive oxidation.

The prealloy is then reduced to particulate form. Preferably the prealloy is particulated by atomizing, such as by jet atomizing in which a stream of gas of suitable velocity impinges on a thin stream of molten prealloy causing formation of small droplets which solidify into pellets. The melt may also be particulated by disc atomizing in which a thin stream of molten prealloy is intercepted by a spinning disc of sufiicient velocity to cause formation of droplets which solidify upon being flung off the disc into pellets. All or a majority of the pellets should be of a size capable of at least passing about a number -20 mesh screen (US. Standard Sieve Series). Fine particles, e.g., less than about l00 mesh, are preferred, but not essential.

Said prealloy is then intimately and homogeneously contacted as aforesaid with at least one metalloid selected from the Group VB elements in an amount of from about 0.05 to about 25.0 weight percent. Preferably, the Group VB additive metalloids will be selected from arsenic, antimony and bismuth, in a percentage amount (based on the total weight of the final alloy) within the broad and preferred ranges indicated below.

The term metalloid, as used herein, refers to the Group VB elements of antimony, arsenic and bismuth.

The contacting of the lead base prealloy particles with the metalloids may be accomplished using conventional or other means, preferably so as to substantially cover or coat or surround the prealloy pellet with the metalloid as much as possible. For example, the metalloid may be prepared in particulate form, such as by atomizing or grinding, and physically homogeneously admixed with the prealloy pellets. For proper contacting a majority of such particles of the metalloid should be of a mesh size of about 200 mesh, preferably 325 mesh. Such element may also be in the form of a lead alloy. For example, 20 weight percent of a lead alloy containing 15 weight percent bismuth, the balance being essentially lead, may be admixed with a prealloy to yield a final alloy containing 3 weight percent bismuth. To accomplish or aid in such mixing a filming liquid, e.g., ethylene glycol or stearic acid may be employed to wet the surfaces of the particles for better adherence. Alternatively, the Group VB elements may be vaporized for deposition on the prealloy particles by condensation. Other suitable means may also be employed.

A final creep resistant lead base is then prepared so as to provide an essentially insoluble intermetallic compound finely dispersed throughout a lead matrix. This may be accomplished by one of various ways including hot working the final alloys, or by cold working the final alloy with an accompanying heat treatment step. In some cases, heat treatment may be beneficial subsequent to hot working also.

Working may be carried out using techniques and equipment known to those skilled in the art, such as by extruding, and/or compacting, rolling or forging. Such working may be done at room temperatures or at elevated temperatures up to about 400 F. to accomplish beneficial diffusion, preferably from 200 to 350 F. Where cold (room temperature) working is employed, heat treatment is normally desirable to aid dilt'usion of the metalloid and provide dispersion of the resulting intermetallic compound in the lead matrix. Such heat treatment may be accomplished before or after the mixture is worked at 5 temperatures up to about 400 F., preferably from about 200 F. to about 350 F., for up to about hours. Heat treatment beyond this range should be avoided to minimize agglomeration of the intennetallic particles. Where hot working is employed, heat treatment may be unnecessary and excessively high temperatures or long times may even in some cases be including percent elongation (%E), tensile strength (TS) and tensile yield strength at 0.2 percent deviation from the modulus (TYS) were measured for each sample in the as-extruded and heat treated conditions. Samples of the extruded alloys were also subjected to tensile creep at 75 F. for 100 hours at l,000 p.s.i. and the percent creep (%Creep) determined. For comparison, extruded rods of the original lead-calcium prealloy pellets and also of a lead base alloy containing 0.03 percent calcium, 0.06 percent copper, 0.01 percent silver, the balance being essentially lead, were similarly tested. The results are shown in table I. 7

TABLE I.-HOT WORKING As-extruded300 F., Heat treated-d6 hours,

)6 1.0.rn. 400 F.

Per- 100 p s 1 Per- Per- 100 p.s.i. Per- Pre-alloy Metalcent cent cent cent element lold E TIB TB creep 1 E T18 T8 creep Example Number:

Comparative .03 Ca, .06 None. 48 14 26 5 2. 75

Cu, .01 Ag. .5 Ca .do 42 18 61 1. 81 27 17 Broke 5 Ca 3 BL 26 29 49 .29 30 19 33 D0. 50a 3B1"... 29 26 46 .16 39 19 32 Do. .5 Ca 3 Sb..." 12 57 73 .025 26 30 46 .07.

l The balance being essentially lead.

1 At 1,000 psi. for 100 hours at 75 F.

3 Percent creep after 10 hours-third stage creep started immediately.

detrimental to the creep resistance of the final lead base alloy.

One method of working found particularly desirable is by 3 extruding the mixture of prealloy and metalloid to provide a final alloy extruded article. In this process the mixture is normally preheated to a temperature from about 200 F. to about 400 F. and placed in an extrusion container usually kept at a temperature of from about 70 F. to about 350 F. Extrusion is accomplished by subjecting said mixture to a sufficient displacement pressure to express it through a die having the desired extrusion aperture. if desired the mixture may be initially compacted prior to extrusion.

The novel lead base alloy of the present invention soprepared has excellent creep resistance as compared to, e.g., conventional lead alloys, e.g., those containing only calcium or antimony. This is apparently due to the fine dispersion in the lead matrix of highly stable intermetallic compound particles as formed from the novel sequence of process steps herein and by contact of the solid soluble alkali or alkaline earth component from Groups IA and 11A in the lead base prealloy with the metalloid component from Group VB. For example, magnesium and antimony form the intermetallic compound, Mg sb lithium and bismuth form the intermetallic compound, Li Bi; calcium and arsenic form Ca As and sodium and antimony form Na sb.

The following examples serve to further illustrate the application and utility of the present invention, but are not intended to limit it thereto.

EXAMPLES l-3 A lead melt containing 0.5 weight percent calcium was The data of table I shows that alloys of the present invention made by the method of the present invention, while maintaining comparable strength properties, have substantially increased creep resistance, as indicated by the much lower creep values, than conventional lead base alloys. As previously disclosed, heat treatment after hot working (extrusion at 300 F.) is detrimental to creep resistance in some cases (examples l and 2 However, such heat treating experimentation also shows the extreme stability of the dispersion of the calcium-antimony intermetallic, Ca sb (example 3) and, therefore, the continued high creep resistance, even after extensive heat treatment, of the lead base alloy containing calcium and antimony within the present invention.

EXAMPLES 4-7 A lead melt containing 1.0 weight percent magnesium was prepared conventionally and jet atomized in air to produce lead base-magnesium prealloy pellets having a particle size of less than about 20 mesh. One sample was admixed with about 3 weight percent fine (about 200 mesh) bismuth powder (example 4). Another sample was admixed with about 20 weight percent of lead alloy pellets containing about 15 weight percent bismuth (example 5). Thus the final alloy contained about 3 weight percent bismuth. The lead-bismuth prealloy was conventionally prepared and pelletized by jet atomizing. A third sample of lead-magnesium prealloy pellets was admixed with about 3 weight percent fine (about 200 mesh) antimony powder (example 6). Still a fourth sample was admixed with about 3 weight percent very fine (about 325 antimony powder (example 7).

Each sample was placed in a la-inch diameter extrusion container at F. and extruded at A f.p.m. into A-inch diameter rod. Portions of each rod were then heat treated for 16 hours at 225 F. Rod samples in the as-extruded and heat treated conditions were subjected to tensile creep at 75 F. for hours at 1,000 psi. and the percent creep determined. lThB results are shown in table II.

TABLE II.COLD WORKING lets was physically admixed with about 3 weight percent fine (about -200 mesh) antimony powder (example 3).

Each sample mixture was placed in a 96-inch diameter extrusion container heated at 300 F. and extruded at ya-foot per As ex- Heat truded treated i.p.m. 16 hours,

Pre-alloy Metalpercent percent element loid 1 creep creep minute (f.p.m.) into a %-inch diameter rod. Portions of each rod were then heat treated for 16 hours at 400 E l roperties 1 Balance being essentially lead. 7 Sb powder-average mesh size of 200 m. 3 Sb powder-average mesh size of -326 m.

Unlike examples l-3, examples 4-7 were cold worked (extrusion at 75 F.) allowing less difiusion of the metalloid in the lead matrix. This accounts for the relatively high creep of ex- 2. A process for preparing a creep resistant lead base alloy which comprises the steps of:

a. dissolving in molten lead at least one alkali or alkaline earth additive metal selected from the group consisting of, the following elements in an amount by weight, within the 6 following corresponding ranges:

Alkali or Alkaline Earth Metal Range in Percent Weight b. particulating the mass from the molten form to provide a prealloy of the additive metal with lead, c. intimately and homogeneously contacting said solid, particulate prealloy with at least one metalloid selected from 7 the group consisting of the following elements in an amount by weight within the following corresponding ranges: amples 6 and 7 in the as-extruded condition. In all cases heat treatment at moderately low temperatures of 225 F. for 16 5 Range in Percent hours was highly beneficial and the creep resistance of the Memlhid Weight lead base alloys within the present invention was substantially increased. Antimony 0.05-12.0

Portions of the'examples 4-7 rods were heat treated for 16 f hours at 325 F. and 400 F. Each was subjected to tensile l0 Bl'mmh creep at 75 F. for 100 hours at 1,000 p.s.i. and the percent creep determmed' The results are Shown m table d. diffusing said metalloid into the prealloy to provide an es- TA 1] sentially insoluble intermetallic compound finely l dispersed throughout a final creep resistant lead base alloy. percentage, 3. The process of claim 2 wherein alkali or alkaline earth Heaureazed Heanr ai d additive metal selected is in an amount within the following Example No. 325 F. l6 hours 400 F. l6 hours range f h respective l:

4 013 036 Alkali or Alkaline Range in Percent 5 014 Earth Metal Weight 6 0.07 0.09 1 0.09 0.10

Calcium 0.05 0.5 Lithium o.os o.s

Magnesium 0.5-l .0 As table Ill indicates, heat treatment at temperatures above Sodium 0.54.5 about 300 F. is in most cases beneficial as shown by a comparison of the as-extruded Creep of table II with the Creep at 325 F. and 400 F. of table [II for a particular ex- 3 and the metalloid selected is in an amount within the following ample. However, heat treatment at such higher temperatures range for the respective metal: may not in all cases produce the enhanced results (example 5). This is due apparently to agglomeration of the intermetal- Range in Pmem P Metalloid Weight The present invention may be modified or changed without 3 5 departing from the spirit or scope thereof and it is understood Amman), 0J4) that the invention is only limited as defined in the appended Arsenic c|aim Bismuth 0140.00

We claim:

1. A process for preparing a creep resistant lead base alloy 40 h V H A A 7 whlch F the steps 4. The process of claim 2 wherein the selected metalloid is a. dlSSOlVlllg lll molten lead at least one alkalt or alkaline antimony earth additive meta] selectefd f IA and Group 5. The process of claim 2 wherein, in step (d) the diffusion of the Mendeleeff f Chan m an amount of is accomplished by hot working the solid prealloy and metalf to about we'ght percent loid mixture at a temperature within the range of from about b. partlculatlng the mass from the molten form to provide a 5 0 F. to about F P'Q of the addmve mew] leadi 6. The process of claim 5 wherein the hot working is accomc. intimately and homogeneously contacting said solid, parpushed by extrusion of the prea]|oy mem"oid mixture.

ticulate prealloy with at least one metalloid selected from The process of claim 5 wherein the hot working is cam-ed Group VB of Said Psfl'fldiqchm in an amount of from out at a temperature within the range of from about 200 F. to about 0.05 to about 25.0 weight percent, about F d. diffusing said metalloid into the prealloy to provide an es- 8 The process of m 2 wherein, in step (d) the diffusion semiany insoluble mtermetan'c Fompound finely is accomplished by heat treating the prealloy and metalloid dispersed throughout a final creep reslstam lead base mixture at a temperature within the range of from about 150 Y- F. to about 400 F. for about 1 to about 20 hours and then cold working said mixture.

9. The process of claim 2 wherein, in step (d) the diffusion is accomplished by cold working the prealloy and metalloid mixture and then heat treating the worked mixture at a temperature within the range of from about F. to about 400 for about lto about 20 hours.

10. The process of claim 9 wherein the cold working is accomplished by extrusion.

11. The process of claim 9 wherein the heat treatment is carried out at a temperature within the range of from about 200" F. to about 350 F.

12. The process of claim 2 wherein, in step (d) the diffusion is accomplished by compacting the prealloy and metalloid mixture and heat treating the mixture at a temperature within the range of from about 150 F. to about 400 for about I to about 20 hours and then cold working said mixture. 0 l3. TheFocess ot cliflm'fwherein, in step (b) the particulating is accomplished by atomizing. 

2. A process for preparing a creep resistant lead base alloy which comprises the steps of: a. dissolving in molten lead at least one alkali or alkaline earth additive metal selected from the group consisting of the following elements in an amount by weight, within the following corresponding ranges: Alkali or Alkaline Range in Percent Earth Metal Weight Calcium 0.01-0.7 Lithium 0.01-0.7 Magnesium 0.01-1.5 Sodium 0.01-2.0 b. particulating the mass from the molten form to provide a prealloy of the additive metal with lead, c. intimately and homogeneously contacting said solid, particulate prealloy with at least one metalloid selected from the group consisting of the following elements in an amount by weight within the following corresponding ranges: Range in Percent Metalloid Weight Antimony 0.05-12.0 Arsenic 0.05-6.0 Bismuth 0.1-20.0 d. diffusing said metalloid into the prealloy to provide an essentially insoluble intermetallic compound finely dispersed throughout a final creep resistant lead base alloy.
 3. The process of claim 2 wherein alkali or alkaline earth additive metal selected is in an amount within the following range for the respective metal: Alkali or Alkaline Range in Percent Earth Metal Weight Calcium 0.05-0.5 Lithium 0.05-0.5 Magnesium 0.5-1.0 Sodium 0.5-1.5 and the metalloid selected is in an amount within the following range for the respective metal: Range in Percent Metalloid Weight Antimony 0.1-6.0 Arsenic 0.5-3.0 Bismuth 0.2-10.00
 4. The process of claim 2 wherein the selected metalloid is antimony.
 5. The process of claim 2 wherein, in step (d) the diffusion is accomplished by hot working the solid prealloy and metalloid mixture at a temperature within the range of from about 150* F. to about 400* F.
 6. The process of claim 5 wherein the hot working is accomplished by extrusion of the prealloy-metalloid mixture.
 7. The process of claim 5 wherein the hot working is carried out at a temperature within the range of from about 200* F. to about 350* F.
 8. The process of claim 2 wherein, in step (d) the diffusion is accomplished by heat treating the prealloy and metalloid mixture at a temperature within the range of from about 150* F. to about 400* F. for about 1 to about 20 hours and then cold working said mixture.
 9. The process of claim 2 wherein, in step (d) the diffusion is accomplished by cold working the prealloy and metalloid mixture and then heat treating the worked mixture at a temperature within the range of from about 150* F. to about 400* for about 1to about 20 hours.
 10. The process of claim 9 wherein the cold working is accomplished by extrusion.
 11. The process of claim 9 wherein the heat treatment is carried out at a temperature within the range of from about 200* F. to about 350* F.
 12. The process of claim 2 wherein, in step (d) the diffusion is accomplished by compacting the prealloy and metalloid mixture and heat treating the mixture at a temperature within the range of from about 150* F. to about 400* for about 1 to about 20 hours and then cold working said mixture.
 13. The process of claim 2 wherein, in step (b) the particulating is accomplished by atomizing. 